The present disclosure relates to semiconductor devices. As one of various scaling techniques to increase the density of a semiconductor device, a multi-gate transistor has been proposed in which a fin-shaped or nanowire-shaped multichannel active pattern (or silicon body) is formed on a substrate and gates are formed on a surface of the multichannel active pattern. Further, as the feature size of a metal-oxide-semiconductor (MOS) transistor decreases, the length of a gate and the length of a channel that is formed below the gate also decrease. As the channel length of the transistor decreases, scattering of carriers (electrons or holes) in the channel may increase and mobility of the carriers may thus decrease. The decrease of the mobility of the carriers may cause obstacles to the improvement of the saturation current of the transistor.